1. Field of the Invention
This invention relates to color cathode ray picture tubes and is addressed specifically to an improved means and process for securing a foil tension shadow mask, sometimes referred to as a flat tension mask (FTM) or simply as a "mask", as all of these terms are taken to have the same meaning in the following paragraphs, to a shadow mask support structure that extends from the inner surface of a faceplate. Color tubes of various types having the FTM can be manufactured by the process including those used in home entertainment television receivers. The process, according to the invention, is of particular value in the manufacture of medium-resolution, high-resolution and ultra-high resolution tubes intended for color monitors.
The use of the FTM and flat faceplate provides many benefits in comparison to the conventional domed shadow mask and correlatively curved faceplate. Chief among these is a greater power-handling capability which makes possible as much as a three-fold increase in brightness. The conventional curved shadow mask, which is not under tension, tends to "dome" in picture areas of high brightness where the intensity of the electron beam bombardment is greatest. Color impurities result as the mask moves closer to the screen and as the beam-passing apertures move out of registration with their associated phosphor elements on the screen. When heated, the tension mask distorts in a manner quite differently from that of the conventional mask. If the entire mask is heated uniformly, there is no doming and no distortion until tension is completely lost; just before that point, wrinkling may occur in the corners. If only portions of the mask are heated, those portions expand and the unheated portions contract resulting in displacements within the plane of the mask; i.e., the mask remains flat.
The FTM is a part of the cathode ray tube front assembly and is located closely adjacent to the faceplate. The front assembly primarily comprises the faceplate with its screen which consists of deposits of light-emitting phosphors, an FTM and support means for the mask. As used herein, the term "FTM", or "mask", means an apertured metallic foil which may, by way of example, be about 0.001 inch thick, or less. The mask must be supported in high tension a predetermined distance from the inner surface of the cathode ray tube faceplate; this distance is known as the "Q-distance". As is well known in the art, the shadow mask acts as a color-selection electrode, or parallax barrier, which ensures that each of the three electron beams lands only on its assigned phosphor deposits.